1. Field of the Invention
The present invention relates to sheet processing apparatuses that perform processing on sheet bundles, and particularly, to a sheet processing apparatus that deforms a folded spine of a booklet, which is made by folding a predetermined number of stacked sheets, so as to enhance stackability and to improve the appearance of the booklet.
2. Description of the Related Art
Generally, when a bundle of 20 or more stacked sheets is folded, a booklet with a curved finish at the folded section is often made. Because such a booklet is insufficiently folded, the open side thereof opposite the folded section tends to open undesirably, resulting in a poor external appearance.
In order to solve this problem, a method and an apparatus for squaring the spine of the folded section (folded spine or back) of such a booklet as an example of a deformation process are provided (see U.S. Pat. No. 6,692,208). By performing such a deformation process on the folded spine of the booklet, the booklet can be tightly folded, making the open side of the booklet less likely to open undesirably and thus providing a booklet with a good appearance.
The configuration of a sheet processing apparatus of related art will be described with reference to FIGS. 17A to 19.
FIG. 17A schematically illustrates a traveling direction of a pressing roller 704 that comes into pressure contact with a folded spine of a booklet so as to deform the folded spine. The pressing roller 704 is located at a receded position in an area where it does not come into contact with a booklet until the booklet is nipped by gripping portions 702 and 703. When the gripping portions 702 and 703 nip and secure the booklet, the pressing roller 704 moves from one end to another end along the folded spine of the booklet while applying pressure to the folded section.
First, as shown in FIG. 17B, a booklet 701 is conveyed by conveying portions 706 and 707 while the folded spine of the booklet 701 acts as the leading edge. The booklet 701 is positioned by bringing the folded spine into abutment with a positioning portion 705. Subsequently, as shown in FIG. 17C, the booklet is gripped by the gripping portions 702 and 703 in a state such that the folded spine protrudes therefrom, and then the positioning portion 705 is moved away from the folded spine. Then, the pressing roller 704 moves while applying pressure to the folded spine of the booklet protruding from the gripping portions 702 and 703. The reason that the folded spine of the booklet 701 gripped by the gripping portions 702 and 703 is made to protrude therefrom is to deform the protruding folded spine by bringing the pressing roller 704 into pressure contact with the folded spine. If the protruding amount from the gripping portions 702 and 703 is too small, the folded spine becomes less deformable since the stiffness thereof increases. If the protruding amount is too large, the folded spine also becomes less deformable since it escapes from the pressing roller 704 during the deformation process. Therefore, the protruding amount is set to an appropriate value.
The term “squaring” refers to a process of angularly deforming the folded spine having a curved shape. FIG. 17D illustrates a state where the booklet having undergone a squaring (deformation) process is being ejected onto a paper output tray 708. FIG. 18A schematically illustrates the folded spine of the booklet when the folded spine is being pressed and squared.
However, because the folded spine of the booklet protruding from the gripping portions 702 and 703 is pressed, edges 709a and 709b of the squared folded spine protrude outward in the thickness direction, as shown in FIG. 18B, resulting in a deteriorated appearance. Furthermore, when the pressing roller 704 is brought into pressure contact with the folded spine, the folded spine deformed outward in the thickness direction may strongly abut on edges 702a and 703a of the gripping portions 702 and 703 gripping the booklet, leaving pressing marks on the booklet.
FIG. 19 illustrates the folded section of the booklet having undergone the aforementioned process in a state where the folded section protrudes from the gripping portions 702 and 703. The folded spine protruding from the gripping portions 702 and 703 deforms outward in the thickness direction of the booklet along a pressing surface of the pressing roller 704. The width of the squared folded spine is greater than the thickness of the actual booklet, resulting in reduced stackability of booklets.
Since the entire folded spine of the booklet protruding from the gripping portions 702 and 703 is subjected to the deformation process, a folded spine 709c of sheets in the central section of the booklet, which do not need to be squared, becomes undesirably deformed if the folded spine 709c protrudes from the gripping portions 702 and 703.
In the present invention, the folded spine can be deformed (squared) into a shape that exhibits a good appearance.